Regional groundwater flow and formation of water quality in G 1 layer throughout the Echigo Plain

Abstract

This paper discusses regional groundwater flow and water quality in a confined aquifer of the G 1 layer distributed throughout the Echigo Plain. The G1 layer is distributed near the ground surface in Nagaoka and reaches a depth of 160 m in Niigata City. The current survey showed groundwater flows relatively actively in Nagaoka, which recharges the G1 layer and flows northward. North of the plain, it was revealed that the high Cl^－ concentration groundwater, which is distributed in Tsubame, Sanjo, and Yoshida, included old groundwater recharged during the last glacial period and young groundwater less than 70 years old. Therefore, new groundwater recharged the aquifer where old groundwater was distributed, and the existence of marine deposits greatly influenced the water quality. The older groundwater possibly remained in the G1 layer due to the decreasing hydraulic gradient from the sea level rise that occurred after the last glacial period ended, and impermeable strata produced by transgression covered the G1 layer.